Baculoviruses are enveloped nucleocapsids which mature both in the nucleus and at the cell surface. The acquisition of an envelope in the cell nucleus requires the synthesis or transport of large quantities of viral envelope substrates to the nucleoplasm. The extent of synthesis and nature of budding of the baculovirus nucleocapsid in the nucleus is a unique phenomenon compared to other virus envelope maturation strategies. Comparison of the structural proteins of the nuclear and cytoplasmic viral forms show major differences in number, size, and in glycosylation and phosphorylation modifications. Studies of the viral genes and their encoded proteins which are unique to either viral form should provide important insights on the molecular basis of viral maturation in the nucleus. The studies proposed are: (a) to map and sequence envelope and nucleocapsid genes that encode proteins that reflect characteristics specific to each form of the baculovirus Autographa californica and which show potential for use as markers; (b) to use these characteristics to study expression, regulation of expression, processing, trafficking and assembly in infected cells. Emphasis will be on the origin and assembly of viral envelopes and the viral maturation process in the nucleus.